When my kids were seniors, I got a note from the HS that they would be studying Genesis as a "literary project". As a parent, I was told I could opt them out, I didn't.
That seemed OK to me. Having some JudeoChristian symbolism in a classroom would not be, in my view, same with some Islamic symbolism, but if they wanted to study the Koran as a literary exercise, fine with me.
Folks who seem to want religion in public schools don't seem to realize it could be a different religion from theirs.